ok, been reading this thread and as i'm in the market now i'll put in my .02.
first the verdict: i'm getting a MBP to reap the benefit of CoreAudio and the generally music-friendly characteristics of OSX. i especially like the "native" MIDI services. aside from working well, i'm naturally drawn to the fact that the OS is designed with music production and performance in mind.
ok, i shared that first to show you i'm not a hater - quite the contrary - but i do have a few gripes, 2 of which can be solved by bootcamping xp (but it's ashame to have to, hence my sharing this), the latter i'm not so sure.
alright. so 2 things i'll miss from windoze are: the little "envelope" icon indicating new mail since last you visitted your inbox. the mac equivalent is the red dot with the number of unread mail in the box, period. but you have to actually visit the inbox to see if there's anything new, which is an unnecessary hardship when it's so easily solved with the new-mail icon. my suggestion for a nice understated (Apple-style) way of conveying new mail without affesting the Leopard template at all would simply be to make the unread-mail circle a different colour when some of it was new since last visit, then it wouldn't even require a new icon. nice and tidy, and performing a small-but-common-sense function, especially for bloggers, which i do when not mixing. so this little inconvenience from my routine (being immediately otified of new mail) irks me, but not enough to elclipse the musical perks.
the other thing, equally small but nonetheless ordinary on windozers, is that i prefer the bottom of the screen be used as an active-window dock, with everything you've got going with its name on a conveniently-togglable button, at a glance. on Macs you have to click and hold on the various programs' icons (Mail, Safari, System etc) to get a scroll list of the active windows in each app, as opposed to an at-a-glance list of buttons at screen bottom. (on windoze machines this area occupies the space occupied by the program dock on the Mac, the contents of which is stacked in the "Start" menu in windoze, a better place for them IMO, and offers the collappsible "quick launch" area for those who want dock access). i know OSX has the area on the right side of the dock for minimised windows, but you can't tell their titles with those little icons, and windoze lists everything active, period, not just minimised, on the dock. i just prefer the windows dock/toolbar to Mac's dock, as gorgeous as Mac's is (and it really is).
the other issue is that when i use the "tap" function on the trackpad to scroll by placing the pointer over the scrollbar arrows, it drifts off the arrow in a few taps. no windows machine i've ever used has done this, and all the MBP's have done it, regardless of trackpad adjustments etc. again, there are workarounds like simply using the scroll keys, or 2-finger scroll, but this is how i'm used to it and more than the annoyance itself, it to me is simply below Apple's normal bulletproof quality standards, and is especially bumming given that even the cheapest windoze machines don't have this problem.
so, i'm getting an MBP as soon as the Penryns hit the street, because my art comes first. but i might very well boot up XP for the daily communications drudgery and only break out Leopard when it's time to rock and roll, but it would be nice to have Leopard tweaked a lil with the dock setup and Mail with a new-mail notification function, and i could embrace it more fully.
as far as the pointer drift when tapping in a single spot, though i can live with it, it really needs to be addressed, and my heightened annoyance at it - aside from the trait itself which is a step down even from my old toshiba rebate-coupon special - is definitely partly due to the "high expectations" factor not only stemming from the cost, but also because i know lots of Mac users and am finally about to join them, in the industry and whom i respect, who swear by Macs.
so i'm getting one, but those are my observations from what i think was a very unbiased comparison. if anything i was biased toward Mac, but these are the few disappointments i had upon actually playing with them, which i'd love to see addressed.